I consider “Ender’s Game” to be one of the classics of science fiction. Despite this, I’ve never once re-read the book in the decade and a half since I picked it up in high school. I’ve never even been tempted to.

When I walked out of the theater after seeing the new movie adaptation, I remembered why.

“Ender’s Game,” based on the best-selling novel by Orson Scott Card, wraps the trappings of a space adventure around a bleak tale of children soldiers and the brutal costs of war. The movie has suffered a little on the way to the big screen, tweaking emotional arcs and trimming away some of the lighter moments, but even at its most powerful and faithful it’s not a pleasant experience. You may get sucked in, but you won’t exactly enjoy being there.

In the movie, Earth is still recovering from an alien invasion that occurred decades before. The adults were completely trounced, so the government decided that young minds had the fluidity and innovation needed to lead armies. Ender, played with haunting intensity by Asa Butterfield, is one of the children training to be a soldier. The movie tilts Ender’s emotional arc in a slightly different direction than the book – he wants to succeed at Battle School more than he did in the book – but Butterfield unifies the character’s thoughtfulness and brutality into a believable and slightly heartbreaking whole.

Many of the book’s nuances are lost in the process of condensing the plot down to a movie, and those that remain are highlighted a little too obviously for comfort. Ender’s complex views on the enemy are nearly squeezed out of the movie entirely, mostly existing in an overly dramatic ending that feels oddly tacked on rather than integral to the plot. It’s vital to the movie’s message, and yet it feels hard to take seriously.

The characters suffer as well. Ender’s siblings become one-note, there mostly for faithfulness than necessity to character or plot, and a lot of the team-building scenes with the other kids in battle school were trimmed for time. In many ways, the movie renders the other students as little more than mere abstractions, chess pieces that Ender must factor into his larger game of survival.

The adults automatically become slightly horrifying in this kind of movie, though Harrison Ford layers enough desperation into his character to make him almost sympathetic. Viola Davis has barely any lines to work with, but she packs each one with as much meaning as she can squeeze in.

The movie does offer some moments of undimmed pleasure, including a few scenes of a simulated combat game that were both clever and fun to watch. The space shots offer their own kind of entertainment, exquisitely rendered enough that they pull you right into the space battle.

Unfortunately, that leaves you far too close and unguarded during the movie’s climax, which thanks to Butterfield’s expression hits like a punch to the gut. It’s supposed to. War hurts, no matter how old you are.